This invention relates generally to a tomographic marking device. More particularly, though not exclusively, the invention relates to a tomographic marking device adapted for use in electron microscopes. The device indicates, through markers projected on the images screen of the microscope, or on a final photograph, the location of the tilt axis of a specimen goniometer stage. The device also indicates the angular rotation of the tilt axis of the specimen goniometer stage on the screen relative to the position of the actual tilt axis of the goniometer stage supporting the specimen. The angular (corkscrew) rotation of the image on the screen is caused by the magnetic lenses of the microscope.
The principal object of the novel tomographic marking device is to provide a visually recordable reference of the location of the electron microscope goniometer tilt axis relative to the image of the specimen being examined and tilted. This information is important and necessary to make accurate tomographic measurements and three-dimensional reconstructed images of the specimen.
Ideally, a tilt axis indicating device would be located within the specimen-holding goniometer stage. This arrangement, however, would require an indicating device of microscopic scale in size, and is, consequently, impractical, if not impossible. Also, locating a tilt axis indicating device within the camera system, below the viewing screen, of the electron microscope would not meet the necessary visibility and positioning requirements of such a device. These requirements are:
1. The tilt axis reference marks should be visible to the operator of the electron microscope.
2. The reference marks should be moveable because the magnified image rotates about the optical axis with changes in magnification, and
3. The device should be reliable to measurements on the order of 0.005 inch.
There are no known devices in the prior art that satisfy the above requirements.